The present invention relates to a support structure for supporting a pressurizer safety and relief valve system above the pressurizer vessel of a pressurized water nuclear reactor power plant.
A pressurizer vessel is used in a pressurized water nuclear reactor power plant to provide relief for coolant overpressure. Usually, such a pressurizer vessel is a vertical, thick walled vessel having a hemispherical top, or dome, and having its bottom end supported by a flanged skirt.
Relief valves are provided for a first level of overpressure protection and safety valves are provided for a second level of overpressure protection. The unit thus comprises a pressurizer relief and safety valve system that has a manifold or header assembly and connections for nozzles in the head of the pressurizer, with piping and discharge outlets provided.
A pressurizer safety and relief valve system which is supported above the pressurizer on columnar supports is described in co-pending application Ser. No. 229,363, now U.S. Pat. No. 4,426,350, dated Jan. 17, 1984, entitled "Improved Valve Support Arrangement for Pressurizer in a Nuclear Power Plant", filed Jan. 29, 1981, in the names of Martin J. Zegar, et al., assigned to the assignee of the present invention, which application is incorporated by reference herein. In said co-pending application, an arrangement for supporting the pressurizer safety and relief valve system is described wherein a common header is secured to the side wall of the pressurizer vessel by the use of columnar supports that are secured to the header and are secured to the pressurizer side wall by the use of lug means. The lug means which are attached to the pressurizer side wall must be capable of supporting the load of the columnar supports and pressurizer safety and relief valve system and could become overstressed for some combinations of loads, and also must be of sufficient dimensions if they are to support the necessary loads.
In the system described in said co-pending application, the main support structure comprises four columnar members equally spaced around the pressurizer vessel and coupled to the lugs on the vessel side wall. A fixed type connection between the lugs and the columnar supports can cause undesirable concentrations of stress and difficulties in fabrication and construction.
It is an object of the present invention to provide a support structure for a pressurizer safety and relief valve system that will ease the stress strain condition of the lugs supporting the system.
It is another object of the present invention to provide a frame for a ring girder, for supporting a pressurizer safety and relief valve system that is sufficiently rigid so as not to bend along a horizontal axis to provide a uniform load on the upper support area of a lug, and sufficiently flexible to provide for possible deflection due to forces caused by temperature variations.